This invention relates to ventilation of turbine components and, more particularly, is generally applicable to ventilation of inter-hub spacings of steam turbines having wheels that are not integral with the shaft of the turbine.
Some steam turbines utilize such large rotors that the turbine wheels, which carry turbine blades, or buckets, at their radially outer portions, are not an integral part of the shaft of the rotor. Each wheel of such turbines typically includes a hub section disposed generally at the radially inner portion of the wheel and each hub section includes a bore therethrough for receiving the shaft of the turbine.
To ensure proper and efficient operation of the turbine, it is required that turbine wheels be maintained at substantially fixed circumferential and axial locations relative to the shaft and relative to other wheels on the shaft. A wheel that is not an integral portion of the shaft may be secured to the shaft by a key and cooperating keyway disposed partially in the shaft and the wheel, and/or an interference shrink fit between the radially inner surface of the hub defining the wheel bore and a cooperating surface of the shaft. It has been suspected that stresses in the wheel hub due in part to shrink fits, in combination with other stresses generated by normal operation of the turbine, e.g. centrifugal stress and thermal stress, may create, in the pressure of a steam/water/oxygen environment in the vicinity of the hub of the wheel, a situation which is conducive to fostering stress corrosion. The precise mechanism which produces stress corrosion is not fully understood. However, it is believed that if accumulation of water, such as may be obtained from condensed steam, along with the concentration of oxygen in steam and/or water which contacts the hub region of the wheel, especially in inter-hub spacings between wheels, is minimized, then the probability of stress corrosion occurring will be reduced, if not eliminated. Since it is critical that substantially all steam follow the designed main steam flow path through a turbine in order to obtain maximum efficiency, any attempt to alleviate the aforementioned problems should do so with minimum interference with the main steam flow path.
Accordingly, it is an object of the present invention to reduce and/or eliminate build-up of oxygen, or other non-condensible gas (such as carbon dioxide), concentration in the hub region of a turbine wheel wherein the wheel is not integral with the shaft of the turbine.
Still another object of the present invention is to provide a method and means for reducing the accumulation of water in the hub region of a turbine wheel, especially in inter-hub spacings between wheels, wherein the wheel is not integral with the shaft of the turbine.
It is another object of the present invention to provide a method and means for reducing the accumulation of water in the hub region of a turbine wheel, without affecting steam flow through the main steam flow path of the turbine, wherein the wheel is not integral with the shaft of the turbine.